Characterization of hemicellulosic fractions from spelt hull extracted by different methods

Arabinoxylans (AXs) from spelt hull were extracted by three different alkaline methods and by two methods with several modalities and two organic acids. The first method enabled to extract 1.4% of the water-extractable AXs (WE-AXs) of the hull with molecular weight (MW) of 5400 g/mol and arabinose to xylose (A/X) ratio of 0.55. The two successive extractions with 2% alkaline peroxide hydrogen at 60 °C during 4 h enabled to extract 20.4% of the water-unextractable AXs (WU-AXs) of the hull. Those fractions had MWs of 6800–7800 g/mol and 227 700–274 600 g/mol and A/X ratios of 0.32 and 0.45. The second method with 2% alkaline peroxide hydrogen at 50 °C during 24 h enabled to extract 25.4% of the hemicelluloses of the hull. The two AX populations had MW of 9200–11 400 g/mol and 256 800–273 200 g/mol with an A/X ratio of 0.36. The third method with NaOH gave the highest yield, 41.9% after a 16 h extraction. A/X ratios (0.18) and MWs (two populations of 9300–9500 g/mol) were lower than those of the previous methods. Organic acids method offered insufficient yields and compounds of very low MW (1300–11 300 g/mol). Methods with alkaline peroxide hydrogen enabled to obtain high MWs and high A/X ratios with moderate yields while the NaOH method gave the highest yield efficiency with lower MWs and A/X ratios. Organic acids method did not bring any advantage neither on the yield nor on the MWs of the compounds.